Angular velocity sensor

ABSTRACT

The present invention aims to present an angular velocity sensor having a self diagnosis function.An angular velocity sensor of the present invention includes a driving part for stably vibrating a driving part of a sensor element having a driver part and a detector part for detecting an angular velocity and detection means for detecting the angular velocity of the sensor element and obtains a self diagnosis signal for a malfunction by detecting a mechanical coupling signal obtained at the detection means.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 09/332,162 filed on Jun. 14, 1999, now U.S. Pat. No. 6,244,095,which is a Divisional of U.S. patent application Ser. No. 08/776,443,filed on Apr. 17, 1997 now U.S. Pat. No. 5,939,630, which is a 371 ofPCT/JP96/01445 filed May 29, 1996.

FIELD OF THE INVENTION

The present invention relates to an angular velocity sensor having aself diagnosis function.

BACKGROUND OF THE INVENTION

A conventional tuning fork type angular velocity sensor has a detectingpart comprising detector plates 13 and 14 and a driving part comprisingdriver plates 11 and 12. As shown in FIG. 19, detector plates 13 and 14are located at the top of the driver plates 11 and 12, respectively.Each detector plate 13 and 14 is joined orthogonally to a respectivedriver plate 13 and 14. When an angular velocity is applied to theangular velocity sensor and while keeping the driving part in continuoustuning fork vibration, the angular velocity is detected by the output ofthe detector plates 13 and 14, which vibrate in opposite directions toeach other corresponding to the applied angular velocity.

In an angular velocity sensor in accordance with the prior art, atightly sealed space is formed by a lid 2, which is made of resin. Lid 2is attached at an aperture of a case 1, also made of resin, of which oneend is open, as shown in FIG. 18.

Inside the tightly sealed space, a circuit board 3 and a metallic weightplate 4 are contained. Supporting pins 5 are attached at four cornersinside the case 1, and weight plate 4 and circuit board 3 areelastically supported and fixed by the supporting pins 5. Dampers 6 madeof rubber are attached at the four corners of weight plate 4 for theelastic support. Supporting legs 7 made of resin are put between damper6 and circuit board 3. Supporting pins 5 are compressed at the tipstoward the circuit board 3 side after penetrating dampers 6, supportinglegs 7 and circuit board 3. Thus, circuit board 3 and weight plate 4 areelastically supported and fixed. A metallic supporting pin 8 is insertedand fixed vertically to weight plate 4, on the circuit board 3 side, asshown in FIG. 19. One end of a metallic supporting pin 9, laid parallelto weight plate 4, is inserted and fixed to supporting pin 8. Thediameter of supporting pin 9 is about one fifth of the diameter ofsupporting pin 8. Furthermore supporting pin 9 is made of metallicmaterial having elasticity, such as: a piano wire, wherein the other endof supporting pin 9 is fixed to a metal plate 10 by soldering.

One end of each of metallic driver plates 11 and 12, which aresandwiching supporting pins 8 and 9 therebetween, is fixed to each sideof metal plate 10. Plate-shaped piezoelectric elements 11 a and 12 a arefixed on the surfaces of metallic driver plates 11 and 12, respectively.In this way, the tuning fork type driving part is formed. The other endsof driver plates 11 and 12 are twisted orthogonally relative topiezoelectric elements 11 a and 12 a to form detector plates 13 and 14.Other plate-shaped piezoelectric elements 13 a and 14 a are fixed ondetector plates 13 and 14, as shown in FIG. 19. In this way, thedetecting part is formed. The angular velocity sensor is composed of thedriving part and the detecting part.

There is a problem with the conventional angular velocity sensorhowever. Namely, the conventional sensor has no ability to detectinformation about the occurrence of a malfunction of the components, northe ability to send such information, judged to be a malfunction of thecomponents, to the outside (e.g., such that an operator can be notifiedof the malfunction).

The present invention provides a sensor that allows detection fromoutside the sensor of a malfunction in the sensor, resulting frompartial damage to the sensor, that prevents the sensor from performingaccurate angular velocity detection. Accordingly, the present inventionprovides a highly reliable angular velocity sensor.

SUMMARY OF THE INVENTION

To achieve the stated purpose, an angular velocity sensor of the presentinvention includes (1) a sensor element having a driver part and adetector part for detecting an angular velocity, (2) drive meansincluding a driver circuit for supplying a driving signal to the drivingpart of the sensor element and a monitor circuit to which a monitorsignal is supplied from the sensor element and stably driving andvibrating the driver part of the sensor element by applying the outputof the monitor circuit to the driver circuit through an AGC (automaticgain control) circuit, (3) detection means including a chargingamplifier to which an output of the detector part of the sensor elementis supplied and a synchronous detector to which an output of thecharging amplifier is supplied through a band pass filter and detectingan output of the band pass filter synchronizing with a driving signalfrom the drive means and outputting an angular velocity signal, and (4)self diagnosis means receiving a mechanical coupling signal obtainedfrom the detection means other than an angular velocity signal,detecting abnormality of the sensor element and outputting a selfdiagnosis signal.

Also, an angular velocity sensor according to another aspect of thepresent invention includes, (1) a sensor element with a vibrating partand detector part for detecting an angular velocity, (2) drive meansincluding a driver circuit and a monitor circuit similar to thatmentioned above, (3) detection means including a pair of currentamplifiers, a differential amplifier and a synchronous demodulator, inwhich the pair of current amplifiers receive outputs from the detectorpart of said sensor element, the differential amplifier amplifies adifference in outputs from the pair of current amplifiers and in whichthe synchronous demodulator detects an output from the differentialamplifier in synchronous with the driving signal from the drive meansand outputs an angular velocity signal, and (4) self diagnosis means foroutputting a diagnosis signal to detect an abnormality of the sensorelement by coupling a signal synchronized with the driving signal to thesynchronous demodulator.

According to the above composition, by making the mechanical couplingsignal always obtained from the detection means as a signal for selfdiagnosis, whether the angular velocity signal is in a state to bedetected normally or not can be easily checked. Also as the mechanicalcoupling signal is always generated, it is unnecessary to independentlyprovide means for generating the mechanical coupling signal.Accordingly, not only is the composition very simple and highly reliablefor self diagnosis, but it also makes it possible to know when thecharacteristics of the sensor become stable after the sensor starts towork so that sensor output information can be utilized at its earliestpossible time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an angular velocity sensor in accordancewith a first exemplary embodiment of the present invention.

FIG. 2 shows waveforms at various points of the angular velocity sensorof FIG. 1.

FIG. 3 is a block diagram of an angular velocity sensor in accordancewith a second exemplary embodiment of the present invention.

FIG. 4 shows waveforms at various points of the angular velocity sensorof FIG. 3.

FIG. 5 is a block diagram of an angular velocity sensor in accordancewith a third exemplary embodiment of the present invention.

FIG. 6 shows waveforms at various points of the angular velocity sensorof FIG. 5.

FIG. 7 is a block diagram of an angular velocity sensor in accordancewith a fourth exemplary embodiment of the present invention.

FIG. 8 shows waveforms at various points of the angular velocity sensorof FIG. 7.

FIG. 9 is a block diagram of an angular velocity sensor in accordancewith a fifth exemplary embodiment of the present invention.

FIG. 10 shows waveforms at various points of the angular velocity sensorof FIG. 9.

FIG. 11(a) is an expanded squint view of an essential part of theangular velocity sensor of FIG. 9.

FIG. 11(b) is a cross sectional view of the essential part of theangular velocity sensor of FIG. 9.

FIG. 11(c) is an equivalent circuit diagram of the angular velocitysensor of FIG. 9.

FIG. 12 is a circuit diagram showing a circuit configuration of theprincipal part of the angular velocity sensor of FIG. 9.

FIG. 13 is a block diagram of an angular velocity sensor in accordancewith a sixth exemplary embodiment of the present invention.

FIG. 14 is a circuit diagram of the essential part of the angularvelocity sensor of FIG. 13.

FIG. 15 shows waveforms at various points of the angular velocity sensorof FIG. 13.

FIG. 16 is a block diagram of an angular velocity sensor in accordancewith a seventh exemplary embodiment of the present invention.

FIG. 17 shows waveforms at various points of the angular velocity sensorof FIG. 16.

FIG. 18 is a squint view for assembling an essential part of an angularvelocity sensor in accordance with the prior art.

FIG. 19 is an expanded squint view of an essential part of the prior artangular velocity sensor of FIG. 18.

FIG. 20(a) is a circuit diagram of an angular velocity sensor inaccordance with an eighth exemplary embodiment of the present invention.

FIG. 20(b) shows a cross-sectional view of the angular velocity sensorof FIG. 20(a) taken across W—W.

FIG. 20(c) shows a detailed current distribution in the W—W crosssectionof FIG. 20(b).

FIG. 21 shows waveforms at various points of the angular velocity sensorof FIG. 20(a).

FIG. 22 is a circuit diagram of an angular velocity sensor in accordancewith a ninth exemplary embodiment of the present invention.

FIG. 23 shows waveforms at various points of the angular velocity sensorof FIG. 22.

FIG. 24 is a circuit diagram of an angular velocity sensor in accordancewith a tenth exemplary embodiment of the present invention.

FIG. 25 shows waveforms at various points of the angular velocity sensorof FIG. 24.

FIG. 26(a) is a circuit diagram of an angular velocity sensor inaccordance with an eleventh exemplary embodiment of the presentinvention.

FIG. 26(b) shows a detailed current distribution in the W—W crosssectionillustrated in FIG. 26(a).

FIG. 27 shows waveforms at various points of the angular velocity sensorof FIG. 26(a).

FIG. 28(a) is a circuit diagram of an angular velocity sensor inaccordance with a twelfth exemplary embodiment of the present invention.

FIG. 28(b) shows a cross-sectional view of the angular velocity sensorof FIG. 28(a) taken across W—W.

FIG. 29(a) shows waveforms at various points of the angular velocitysensor of FIG. 28(a) before an adjusting operation.

FIG. 29(b) shows waveforms at various points of the angular velocitysensor of FIG. 28(a) during an adjusting operation.

FIG. 29(c) shows waveforms at various points of the angular velocitysensor of FIG. 28(a) after an adjusting operation.

FIG. 30 is a circuit diagram of an angular velocity sensor in accordancewith a thirteenth exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION First Exemplary Embodiment

FIG. 1 is a circuit diagram of an angular velocity sensor in accordancewith a first exemplary embodiment of the present invention. An AC signalof about 1 Vp-p and 1.5 kHz is applied to a piezoelectric element 11 aof a driver plate 11 from a driver circuit 15. Accordingly, driverplates 11 and 12 start a tuning fork vibration inward and outwardagainst a supporting pin 9 as a center. A voltage proportional to theapplied signal is induced at a piezoelectric element 12 a of a driverplate 12 by the tuning fork vibration and becomes a monitor signal shownas waveform A in FIG. 2 (corresponding to point A in FIG. 1), afterpassing a current amplifier 16 and a band pass filter 17. This signal isfed back to the driver circuit 15 through a full wave rectifier 18 andan AGC circuit 19 and thus a driving signal is automatically controlledin its amplitude.

In the detecting part of the sensor, when piezoelectric elements 13 aand 14 a detect an angular velocity, both piezoelectric elements 13 aand 14 a output angular velocity signals of +Q. These angular velocitysignals are shown in FIG. 2 as waveforms B and C, respectively. Theseangular velocity signals are then synthesized at point D, shown in FIG.1, thus becoming an angular velocity signal shown in FIG. 2 as waveformD. Angular velocity signal D is outputted from an output terminal 24after passing through a charging amplifier 20, a band pass filter 21, asynchronous detector 22 and a low pass filter 23. The angular velocitysignals at points E, F and G shown in FIG. 1 are shown in FIG. 2 aswaveforms E, F and G, respectively.

In the exemplary embodiment, although detector plates 13 and 14 have tobe set orthogonally relative to driver plates 11 and 12, it isessentially difficult to put them in true orthogonal directions andmoreover it is impossible to make piezoelectric elements 13 a and 14 aexactly the same in size and attaching configuration to detector plates13 and 14. As a result, piezoelectric elements 13 a and 14 a alwaysgenerate mechanical coupling signals, shown in FIG. 2 as waveforms B andC, other than the angular velocity signals described above. In thiscase, piezoelectric elements 13 a and 14 a are pasted on the same sidesurfaces of detector plates 13 and 14 and the centers of gravity ofdetector plates 13 and 14 deviate a little toward the sides withpiezoelectric elements 13 a and 14 a. Therefore, when driver plates 11and 12 make a tuning fork vibration, for example when they open outward,they open leaning toward the sides of piezoelectric elements 13 a and 14a. Accordingly, mechanical coupling signals generated at piezoelectricelements 13 a and 14 a are in a reciprocal phase as shown in FIG. 2 aswaveforms B and C. Therefore, when the mechanical coupling signals aresynthesized at point D shown in FIG. 1, the synthesized mechanicalcoupling signal becomes small. The synthesized mechanical couplingsignal is amplified at a charging amplifier 20 and an amplifier 25,rectified at a rectifier 26 and then the signal level is judged at ajudge circuit 28 and the judged result is outputted from a signal outputterminal 29. The signals at points H, I and J shown in FIG. 1 are shownin FIG. 2 as waveforms H, I and J, respectively. When signal I outputtedfrom filter 27 is between level “a” and level “b”, the output of judgecircuit 28 is in a low level as shown in FIG. 2 as waveform J and isoutputted from terminal 29.

When, for example, detector plate 14 shown in FIG. 1 is damaged or itslead wire is broken, both the angular velocity signal and the mechanicalcoupling signal from piezoelectric element 14 a become zero after themalfunction, as shown in FIG. 2 as waveform C. As a result, only amechanical coupling signal from piezoelectric element 13 a appears atpoint D shown in FIG. 1, and it becomes a much larger mechanicalcoupling signal than when detector plate 14 was not damaged or its leadwire was not broken. Therefore, the output of filter 27 becomes largerthan level “a” shown in waveform I of FIG. 2 and a high level signal isoutputted from judge circuit 28 as shown in FIG. 2 as waveform J. Whenboth detector plates 13 and 14 are damaged or both lead wires arebroken, the output of filter 27 becomes smaller than level “b” shown inwaveform I of FIG. 2 and a high level signal is also outputted fromjudge circuit 28 as shown in FIG. 2 as waveform J. When such a highlevel signal is outputted, information that the angular velocity sensoris malfunctioning is transmitted.

Second Exemplary Embodiment

FIG. 3 is a circuit diagram of an angular velocity sensor in accordancewith a second exemplary embodiment of the present invention. In thisexemplary embodiment, a synchronous detector 30 is inserted betweenamplifier 25 and filter 27. A synchronous detection is executed by usinga feedback signal from the feedback circuit of a driving signal. Such afeedback signal is a phase shifted signal from the signal at point Athrough phase shifter 31 shown in FIG. 3. In other words, because themechanical coupling signal flowing into amplifier 25 contains an angularvelocity signal, the level of the mechanical coupling signal is broughtclose to a correct value by canceling the angular velocity signal. Thesignal shown in FIG. 4 as waveform A flowing at point A shown in FIG. 3is delayed by 90 degrees at phase shifter 31. If the output fromamplifier 25 is detected to be synchronized with a signal H delayed by90 degrees (shown in FIG. 4 as waveform H), the angular velocity signalis canceled as shown in FIG. 4 as waveform 1. Therefore, it is possibleto bring the mechanical coupling signal level inputted to filter 27close to a correct value.

Third Exemplary Embodiment

FIG. 5 is a circuit diagram of an angular velocity sensor in accordancewith a third exemplary embodiment of the present invention. In thisexemplary embodiment, when the mechanical coupling signals outputtedfrom piezoelectric elements 13 a and 14 a are added at point D, shown inFIG. 5, the sum is made to be zero as an initial setting. While the sumsare not zero in the first and second exemplary embodiments, in the thirdexemplary embodiment, the sum of the mechanical coupling signalsoutputted from piezoelectric elements 13 a and 14 a is made zero bytrimming either detector plate 13 or 14 at the initial setting. It isshown in FIG. 6 as waveform D. For example, at a normal state before amalfunction (e.g., damage to detector 14 or a break of its lead wire),no mechanical coupling signal is generated at point D shown in FIG. 5.However, after the malfunction, the mechanical coupling signal frompiezoelectric element 14 a is generated and the mechanical couplingsignal appears at point D, as shown in FIG. 6 as waveform D. As aresult, the output of judge circuit 28 is a high level at themalfunction as shown in FIG. 6 as waveform J. A signal informing theangular velocity sensor's malfunction is then outputted from signaloutput terminal 29 through a logical sum circuit 32, as shown in FIG. 6as waveform L. In this exemplary embodiment, a feedback signal from thedriver circuit 15, that is an output of full wave rectifier 18, issupplied to logic sum circuit 32 through judge circuit 33. The angularsensor informs the malfunction via signal output terminal 29, even whendriver plates 11 and 12 are not driven. Accordingly, the driving signalis supplied to logical sum circuit 32 through judge circuit 33. Judgecircuit 33 outputs a high level when the feedback signal is zero becausedriver plates 11 and 12 are not driven and outputs a signal informingthe malfunction from signal output terminal 29 through logical sumcircuit 32.

In the composition where the output of charging amplifier 20 is inputtedto amplifier 25 as a self diagnosis means as shown in the first, thesecond and the third exemplary embodiments, when a signal exceeding aninput range of synchronous detector 22 is inputted from band pass filter21, the output signal at output terminal 24 sometimes varies although noangular velocity signal is added. In this case, it is desirable tochange the composition to input the output signal of band pass filter 21to amplifier 25, to detect saturation of synchronous detector 22 as acriterion for judging and to match a time constant of filter 27 with atime constant of low pass filter 23.

Fourth Exemplary Embodiment

FIG. 7 is a circuit diagram of an angular velocity sensor in accordancewith a fourth exemplary embodiment of the present invention. Also inthis exemplary embodiment, an initial setting is made so that when themechanical coupling signals from piezoelectric elements 13 a and 14 aare added, their sum becomes zero by trimming either detector plate 13or 14, like in the third exemplary embodiment. The signal frompiezoelectric element 13 a is amplified at a charging amplifier 20 a,the signal from piezoelectric element 14 a is amplified at a chargingamplifier 20 b, and they are added at adder 34. Adder 34 outputs a sumsignal that is outputted from output terminal 24, after being processed,as an angular velocity signal. Subtracter 35 subtracts the output ofcharging amplifier 20 b from the output of charging amplifier 20 a andthe result, after being processed, is outputted from signal outputterminal 29 as a self diagnosis signal. Waveforms at the indicatedpoints in FIG. 7 are shown in FIG. 8. Amplifier 25, rectifier 26 andfilter 27 can be omitted. Although the explanation was made using atuning fork type angular velocity sensor, it is possible to detect amalfunction using the mechanical coupling signal in various other typesof angular velocity sensors; e.g., triangular prism type, solid cylindertype, tuning fork type or tubular type; because such other types ofangular velocity sensors also generate a mechanical coupling signal.

Fifth Exemplary Embodiment

FIG. 9 is a circuit diagram of an angular velocity sensor in accordancewith a fifth exemplary embodiment of the present invention.

An alternating signal of about 1 Vp-p and 1.5 kHz is applied from adriver circuit 15 to a piezoelectric element 11 a of a driver plate 11.Driver plates 11 and 12 start tuning fork vibration inward and outwardagainst a supporting pin 9 as a center. A voltage proportional to anapplied signal is induced at a piezoelectric element 12 a of driverplate 12 by tuning fork vibration and is outputted from point A as amonitor signal after passing through a current amplifier 16 and a bandpass amplifier 17. The output signal is shown in FIG. 10 as waveform A.This signal is fed back to a driver circuit 15 through an AGC (AutomaticGrain Control) circuit 19 and the level of the driving signal iscontrolled to always be constant at point A. In the detecting part ofthe circuit, the signals from piezoelectric elements 13 a and 14 a aresynthesized at point D and the synthesized signal is supplied to acharging amplifier 20. The monitor signal from point A synchronized witha tuning fork vibration is attenuated by an attenuator 36 and issupplied to a non-inverted input terminal of a charging amplifier 20after passing through an injector 37. The output of charging amplifier20 is outputted from an output terminal 24 after passing through a bandpass filter 21, a synchronous detector 22 and a low pass filter 23.Signal waveforms at point I (the output of attenuator 36), H (the outputof injector 37), E (the output of charging amplifier 20), F (the outputof synchronous detector 22) and G (the output of low pass filter 23) areshown in FIG. 10 as waveforms I, H, E, F and G, respectively.

In this exemplary embodiment, piezoelectric element 13 a detecting anangular velocity is glued on a detector plate 13 by an adhesive 8. Asilver electrode 13 b is formed on piezoelectric element 13 a as shownin FIG. 11(a).

Detector plate 13, piezoelectric element 13 a and silver electrode 13 bform a parallel plate capacitor as shown in FIG. 11(b) and itsequivalent circuit is shown in FIG. 11(c). The capacity of a capacitorformed by piezoelectric element 13 a is expressed by equation (1).

Cs 1=ε*S/d  (1)

ε: permittivity of piezoelectric element,

S: area of the electrode, and

d: thickness of piezoelectric element.

Similarly, the capacity of a capacitor formed by piezoelectric element14 a is expressed by equation (2).

Cs 2=ε*S/d  (2)

ε: permittivity of piezoelectric element,

S: area of the electrode, and

d: thickness of piezoelectric element.

There are the following relations between the sensitivities ofpiezoelectric elements detecting an angular velocity and capacities Cs1and Cs2 expressed by equations (1) and (2).

The sensitivity is proportional to area S and capacity C is proportionalto area S; therefore, the sensitivity is proportional to capacity C.Therefore, if a capacity variation can be detected, a sensitivityvariation can be conjectured and it is therefore possible to detect asensitivity abnormality.

Now, monitor signal A at point A is attenuated at attenuator 36, asshown in waveform I of FIG. 10, and supplied to injector 37. Injector 37is composed of, for example, a capacitor and a resistor shown in FIG.12. A signal phase shifted against monitor signal A, as shown inwaveform H of FIG. 10, is supplied to a non-inverted input terminal ofcharging amplifier 20. However, because the inverted input and thenon-inverted input of charging amplifier 20 have virtually the samepotential, the signal from injector 37 supplied to the non-invertedinput terminal also appears at the inverted input terminal of chargingamplifier 20, as shown by waveform D in FIG. 10.

As a result, a displacement current ID shown by waveform D (broken line)of FIG. 10 appears at capacity components Cs1 and Cs2 of piezoelectricelements 13 a and 14 a connected to the inverted input terminal and avoltage shown by waveform E of FIG. 10 is outputted from chargingamplifier 20. The output voltage “ve” at point E is expressed byequation (3).

ve=Vm*α*(1/CO)*(Cs 1+Cs 2)*ID∠ø  (3)

ve: output voltage E (Vp-p) of charging amplifier,

Vm: monitor voltage (Vp-p),

α: attenuation factor (0<α<1) of attenuator 36,

∠ø: phase shift (0°<ø<90°) by injector 37,

CO: feedback capacity (pF) of charging amplifier 20, and

ID: displacement current (pA).

Signal Vout obtained from output terminal 24 is expressed by equation(4).

Vout=A*D*Vm*α*(1/CO)*(Cs 1+Cs 2)*ID*sin ø  (4)

D: detection constant of synchronous detector 22 and

A: dc gain of low pass filter 23.

Signal E shown in FIG. 10 is phase shifted by ∠ø against monitor signalA and is detected at synchronous detector 22 after being amplified atband pass filter 21. Here, only a signal component corresponding to thephase shift is extracted, amplified at low pass filter 23, and outputtedfrom terminal 24 as a dc offset component. Usually, it is good to adjustthe offset voltage of the output, for example 2.5 V, considering this dcoffset component.

From equation (3), because signal E shown in FIG. 10 is proportional tocapacity Cs1 or Cs2 of piezoelectric element 13 a or 14 a for angularvelocity detection, respectively, for example, when a disconnectionoccurs at point B or C shown in FIG. 9, there is a signal levelvariation as shown by waveforms E and F of FIG. 10 and as a result, thevoltage level at output terminal 24 varies. This level variation canindicate an abnormality, which abnormality is judged as a sensormalfunction by, for example, a comparison to a threshold value of thelevel variation.

Because the input signal of injector 37 is obtained from the monitorsignal A of the drive circuit 15 and the output signal is applied to theinput terminal of charging amplifier 20, whenever any component or anypart of the tuning fork, the drive circuit or the detection circuitmalfunction, a signal appears at output terminal 24 as a variation ofthe dc offset component and it is therefore always possible to detect asensor malfunction.

Sixth Exemplary Embodiment

FIG. 13 is a circuit diagram of an angular velocity sensor in accordancewith a sixth exemplary embodiment of the present invention. In additionto the fifth exemplary embodiment, the input of injector 37 is made tobe selectively connected to the output of attenuator 36 or to theground, by a switch 38 controlled by an external signal from a controlterminal 39. A circuit diagram of an essential part of this embodimentis shown in FIG. 14 and the waveforms are shown in FIG. 15.

Because monitor signal I attenuated at attenuator 36 is usuallydisconnected from injector 37 by switch 38, monitor signal I is nottransmitted to injector 37 and accordingly, the sensor outputs are in anordinary state. When a signal shown by waveform J of FIG. 15, such as acheck signal from a computer, is applied to control terminal 39 shown inFIG. 13, switch 38 closes and signal I from attenuator 36 is transmittedto injector 37. As a result, the signals at each point vary as shown bywaveforms H, D, E and F of FIG. 15 and an offset voltage linked to thecheck signal applied to control terminal 39 is generated at outputterminal 24, as shown by waveform G of FIG. 15. Because this offsetvariation is determined by equation (4) of the fifth exemplaryembodiment, it is possible to know a sensor abnormality by monitoringthis offset variation.

Seventh Exemplary Embodiment

FIG. 16 is a circuit diagram of an angular velocity sensor in accordancewith a seventh exemplary embodiment of the present invention. Thewaveforms are shown in FIG. 17. The seventh exemplary embodiment detailswhen an input terminal of the external signal for controlling the switch38 is used in common with output terminal 29 of judge circuit 28. Judgecircuit 28 monitors, for example, output E of charging amplifier 20 anddetects an abnormal voltage generated by, for example, an abnormal shockor vibration applied to the tuning fork from the outside and outputs asignal to inform an abnormality from terminal 29 to the outside.Although the control signal input terminal of switch 38 is used incommon with output terminal 29, the connect/disconnect logical value isset to be inverse relative to the logical output of the judge circuit28. Therefore, in an ordinary state in which switch 38 is not working,an abnormal voltage generated by an abnormal shock or vibration of thetuning fork applied from the outside is detected and the abnormality isindicated to the outside (by a suitable signal). In a state in which thesensor is checked, by inputting the check signal from terminal 29 andmonitoring the sensor output of terminal 24, a multifunction diagnosisfor malfunction can be made using only one terminal and therefore a highcost performance is realized.

In the case in which connect/disconnect logical value of switch 38 isset to be equal to the logical value of judge circuit 28, it is possibleto transfer to a self diagnosis mode by forcibly working switch 38 bythe logical output of judge circuit 28 and it is possible to keepoutputting a signal as an abnormality detection state at terminal 29until a reset signal for a self diagnosis mode is supplied from theoutside.

Here, although an exemplary embodiment is described in which a sensorworking state is indicated using a sensor signal, it is also possible tooffset adjust the sensor output. In this case, it is preferred to adjustan attenuation amount by attenuator 36 or adjust the offset by adjustingthe phase shift amount by injector 37. It is also possible to compensatefor temperature for the sensor output by using a temperature sensitiveelement so that an attenuation amount or a phase shift amount varieswith temperature.

It is similar, if the output of injector 37 is applied to band passfilter 21 and synchronous detector 22.

Eighth Exemplary Embodiment

FIG. 20(a) is a circuit diagram of an angular velocity sensor inaccordance with an eighth exemplary embodiment of the present invention.FIG. 20(b) shows a cross sectional view of a sensor element 40 of thepresent embodiment cut at the plane normal to the y-axis including lineW—W (denoted by W—W plane or W—W cross section hereinafter). FIG. 20(c)shows detailed current distribution in the W—W cross section of thesensor element 40. In FIG. 20(a), elements which have the same functionas in FIGS. 9, 13 and 16 are denoted by the same reference numerals anda detailed explanation thereto is omitted.

As shown in FIGS. 20(a), 20(b) and 20(c), the sensor element 40 (e.g.,crystal (quartz) tuning fork vibrator) is constructed by directlybonding two crystal tuning fork vibrator pieces 40 a and 40 b at bondingsurface 41 in such a manner that the directions of the electric axes Eof the vibrator pieces 40 a and 40 b are aligned opposite to each otheralong the width direction (along the x-axis direction) of the vibratorpieces. Thus the sensor element 40 has a bimorph structure.

The sensor element is constructed by forming monitor electrode 42,driving electrodes 43, 46 and 47 (see FIGS. 20(a), (b)), and sensingelectrodes 44 and 45, made of metal such as gold, on the appropriatesurfaces of the crystal tuning fork vibrator pieces 40 a and 40 b.

FIGS. 20(b) and 20(c) show the situation when polarity of drivingelectrode 47 is positive (denoted by D+), polarity of driving electrodes43 and 46 is negative (denoted by D−), polarity of sensing electrode 44is negative (denoted by S−) and polarity of sensing electrode 45 ispositive (denoted by S+). Also, monitor electrode 42 is denoted by M.

First, an explanation will be made for individual roles of the circuitcomponents newly introduced in this exemplary embodiment. Turning toFIG. 20(a), current amplifiers 50 and 51, having a phase difference of 0or 180 degrees between input current and output voltage, amplify thesignals from sensing electrodes 45 and 44, respectively. Differentialamplifier 52 amplifies and outputs the difference between the outputs ofcurrent amplifiers 50 and 51. 90 degree phase shifter 53 shifts thephase of the signal outputted from differential amplifier 52 by 90degrees. Capacitor 54 is inserted between the input terminal of currentamplifier 51 and the reference level in order to balance with capacitor37 a which works as an injector. Accordingly, the capacitance value ofcapacitor 54 is set nearly the same as that of capacitor 37 a. By thisconfiguration, even if the charge/discharge current in capacitor 37 a isinduced by the reference level variation owing to the voltage variationof the power source of the sensor and is inputted to current amplifier50, this current balances with the charge/discharge current in thecapacitor 54, so that it is canceled out by differential amplifier 52.As a result, a sensor with high durability against the voltage variationof the power source is obtained. Digital adjusting circuit 63 adjuststhe output level of the sensor.

Next the fundamental operation of the angular velocity sensor shown inFIG. 20(a) is explained. As shown in FIG. 20(a), driven by drivercircuit 15, sensor element 40 starts to vibrate and at the same timegenerates, at its monitor electrode 42, a monitor signal proportional tothe intensity of the vibration. This monitor signal is processed atcurrent amplifier 16 (monitor circuit) and AGC circuit 19 and finally isfed back to driver circuit 15. Thus, driving of sensor element 40 isperformed stably by drive means composed of the closed loop.

The vibration of sensor element 40 is a tuning fork vibration along thex-axis direction with a velocity V as shown in FIG. 20(a). When anangular velocity around the y-axis is applied to the sensor element 40,a Coriolis force Fc=m×V x (where m is a mass of arm) is generated in thecrystal tuning fork vibrator pieces 40 a and 40 b along the z-axisdirection.

Internal current distribution in a W—W cross section of each arm of thesensor element 40 is shown in FIG. 20(c) when the above-mentionedCoriolis force is generated in each arm. As each arm of the sensorelement 40 bends in opposite directions to each other along the z-axis,currents with almost the same amplitudes and opposite polarities aregenerated in sensing electrodes 44 and 45 via monitor electrode 42 anddriving electrodes 43, 46 and 47, as shown in FIG. 20(c).

Currents i_(s) _(⁻) and i_(s) _(⁺) , flowing at each sensing electrode44 and 45, are expressed by formulae (5) and (6), respectively.

i _(s) _(⁻) =−(i _(s) _(⁻) _(−D) _(⁻) +i _(M−S) _(⁻) +i _(D) _(⁺) _(−S)_(⁻) +i _(s) _(⁻) _(−D) _(⁻) )  (5)

i _(s) _(⁺) =(i _(s) _(⁺) _(−D) _(⁻) +i _(M−S) _(⁺) +i _(D) _(⁺) _(−S)_(⁺) +i _(s) _(⁺) _(−D) _(⁻) )  (6)

The currents i_(s) _(⁻) and i_(s) _(⁺) expressed by formulae (5) and (6)are inputted to the current amplifiers 50 and 51 as indicated by d and ein FIG. 20(a). They are converted to voltage outputs and inputted to thedifferential amplifier 52. The output of differential amplifier 52 isinputted to phase shifter 53 where its phase is shifted by 90 degrees.The output of the phase shifter 53 is detected by synchronous detector22 in synchronous with the monitor signal at point ‘a’. The output ofthe synchronous detector 22 is inputted to low pass filter 23 where itsgain and offset are adjusted by digital adjusting circuit 63 and finallyoutputted to output terminal 24.

Operational waveform of each part of the present angular velocity sensorshown in FIG. 20(a) is illustrated in FIG. 21. In FIG. 21, the signalwaveform indicated by ‘a’ corresponds to a monitor signal at point ‘a’monitoring the vibration level of sensor element 40 in a stationaryoperation state. Signal waveforms indicated by ‘b’ and ‘c’ correspond tothe driving signals having opposite phases to each other for drivingsensor element 40. The monitor signal is attenuated by attenuator 36 asshown in the waveform indicated by I. This signal is then supplied,through switch 38, to capacitor 37 a (waveform indicated by m). Here,the switch 38 operates intermittently in response to an externaldiagnosis request signal supplied to control terminal 39 (waveformindicated by o).

Caused by the signal voltage applied to capacitor 37 a, a displacementcurrent with its phase shifted by 90 degrees against the monitor signalis induced (the waveform indicated by n). This displacement current isinputted to the current amplifier 50 and is converted to a voltageoutput (waveform indicated by f).

Each output of current amplifiers 50 and 51 (waveform indicated by f andg respectively) is inputted to differential amplifier 52. Differentialamplifier 52 outputs a waveform indicated by h. The output ofdifferential amplifier 52 is inputted to phase shifter 53 and its phaseis shifted by 90 degrees, resulting in a waveform with the same phase as(indicated by i) or opposite phase relative to the monitor signalindicated by ‘a’. The output waveform of phase shifter 53 (indicated byi) is detected by synchronous detector 22 in synchronous with themonitor signal ‘a’.

Finally, the output from synchronous detector 22 (waveform indicated byj) is inputted to low pass filter 23 where its gain and offset areadjusted by digital adjusting circuit 63 and outputted to outputterminal 24 (waveform indicated by k).

Self diagnosis operation, performed upon request via the externaldiagnosis request signal (waveform indicated by o), generates DCvariation V (indicated in the waveform of k).

In order to enable detection of abnormality of the sensor, the level ofthis DC variation V in ordinary operation is set to a predeterminedvalue by using, for example, an attenuator 36. If an abnormality such aswire breakage happens to occur at point Z in FIG. 20(a) for example, thelevel of DC variation V b e comes different from the above predeterminedvalue (indicated by Z in the waveform of k) while the external diagnosisrequest signal is applied. Thus, the abnormality of the present angularvelocity sensor can be detected by watching the change in the level ofthe DC variation V, using the predetermined V as a threshold.

Although a capacitor is used for the injector in this embodiment, it ispossible to use a resistor also.

Ninth Exemplary Embodiment

FIG. 22 is a circuit diagram of an angular velocity sensor in accordancewith a ninth exemplary embodiment of the present invention. In FIG. 22,elements which have the same function as in FIG. 20(a) are denoted bythe same reference numerals and a detailed explanation thereto isomitted.

As shown in FIG. 22, charging amplifiers 50 a and 50 b withinput-to-output phase shift of 90 or 270 degrees are used in thisembodiment in place of current amplifiers 50 and 51 in FIG. 20(a). Byusing the charging amplifiers 50 a and 50 b, the phase shifter 53 shownin FIG. 20 can be omitted.

Operational waveform of each part of the present angular velocity sensorshown in FIG. 22 is illustrated in FIG. 23. Each waveform shown in FIG.23 is essentially the same as that of FIG. 21. What differs is, thephase of the waveform indicated by f deviates by 90 degrees and thephase of the waveform indicated by i deviates by 180 degrees (orinverted).

Tenth Exemplary Embodiment

FIG. 24 is a circuit diagram of an angular velocity sensor in accordancewith a tenth exemplary embodiment of the present invention. In FIG. 24,elements which have the same function as in FIG. 20(a) are denoted bythe same reference numerals and a detailed explanation thereto isomitted.

In FIG. 24, a timer circuit 61 is introduced which operates in responseto the external diagnosis request signal supplied to control terminal39. With this timer circuit 61, it becomes possible to realize variousfunctions such as to delay, interrupt or extend the external diagnosisrequest signal applied to control terminal 39.

Operational waveform of each part of the present angular velocity sensorshown in FIG. 24 is illustrated in FIG. 25. Each waveform shown in FIG.25 is essentially the same as that of FIG. 21. What differs is, thepulse width length of the waveform indicated by o is shorter and theoutput waveform of timer circuit 61 (waveform indicated by q) is added.

Thus, by inputting short pulse external diagnosis request signalindicated by o, a long continuing signal indicated by q can be obtained,which can keep switch 38 on for a long time. Accordingly, freedom ofinterface design of the external control circuit can be improved.

Eleventh Exemplary Embodiment

FIG. 26(a) is a circuit diagram of an angular velocity sensor inaccordance with an eleventh exemplary embodiment of the presentinvention. In FIG. 26(a), elements which have the same function as inFIG. 20(a) are denoted by the same reference numerals and a detailedexplanation thereto is omitted.

The width of driving electrode 43 a in FIG. 26(a) is set narrower thandriving electrode 43 in FIG. 20(a). Logical sum circuit block 67; whichincludes rectifiers 26 a and 26 b, comparators 28 a and 28 b, andlogical sum circuit 32; works as a judge circuit. It always monitors thelevel of currents d and e outputted from sensing electrodes 45 and 44,respectively, and, if any damage of the sensor happens to occur, outputsa self diagnosis signal to diagnosis signal output terminal 29 a, evenif an external diagnosis request signal is not provided to controlterminal 39.

Operational waveform of each part of the present angular velocity sensorshown in FIG. 26(a) is illustrated in FIG. 27. Each waveform shown inFIG. 27 is essentially the same as that of FIG. 21. What differs isthat, waveforms of currents d and e outputted from sensing electrodes 45and 44 respectively, and waveforms indicated by s, u and w are newlyadded.

Sensor element 40 is in a tuning fork vibration along the x-axisdirection with velocity V as shown in FIG. 26(a). Caused by thisvibration, various currents flow between each electrode in the sensorelement 40 as shown in FIG. 26(b). Currents i_(s) _(⁻) and i_(s) _(⁺) ,flowing at each sensing electrode 44 and 45, are expressed by formulae(7) and (8), respectively.

i _(s) _(⁻) =i ₂ −i ₄ −i ₅ +i ₇  (7)

 i _(s) _(⁺) =i ₁ −i ₃ −i ₆ +i ₈  (8)

Because the magnitudes of i₁ to i₄ are almost the same, i₂ and i₄ anceleach other and i₁ and i₃ also cancel each other in formulae (7) and (8).But as the widths of driving electrodes 43 a and 47 are different, i₅ isnot equal to i₇, and i₆ is not equal to i₈. Accordingly currents i_(s)_(⁻) and i_(s) _(⁺) are finally expressed by formulae (9) and (10).

i _(s) _(⁻) =−i ₅ +i ₇  (9)

i _(s) _(⁺) =−i ₆ +i ₈  (10)

As magnitudes of i₅ and i₆ are almost the same and the magnitudes of i₇and i₈ are also almost the same, the output v of differential amplifier52 is expressed by formula (11) as long as the sensor works normally.

v=V(i _(s) _(⁺) −i _(s) _(⁻) )=0  (11)

But when wire breakage or such abnormality occurs at point y shown inFIG. 26(a) and at a timing Y as shown in FIG. 27, current d becomes zeroso that the output of differential amplifier 52 is no longer keptbalanced, as shown in formula (12) (waveform indicated by h).

v=V(−i _(s) _(⁻) )=V(i ₅ −i ₇)=0  (12)

Voltage v expressed by formula (12) is inputted, via phase shifter 53,to rectifier 26 a and is outputted as a rectified waveform at point s.In the logical sum circuit block 67, the waveform at point s is comparedwith a predetermined threshold value (th) by comparator 28 a. When thewaveform at point s exceeds the threshold value, comparator 28 a outputsa high level shown by u. Thus, even if the external diagnosis requestsignal is not supplied to control terminal 39, logical sum circuit 32outputs a high level as shown by w in FIG. 27 when any abnormalityoccurs in the sensor. Accordingly, abnormalities such as wire breakageor others can be detected always and instantly by watching diagnosissignal output terminal 29 a. Further, in normal operation, the signal atpoint r (i.e., the rectified signal of the signal at point a) is set toexceed the threshold of comparator 28 b, so that comparator 28 b outputsa low level signal at point t. Therefore, when the monitor signal atpoint a is in a normal state, logical sum circuit 32 outputs a low levelsignal to diagnosis signal output terminal 29 a. But when someabnormality in the signal at point a occurs and its value decreasesbelow the threshold of comparator 28 b, the output of comparator 28 bbecomes high and so logical sum circuit 32 outputs a high level signal,thus enabling detection of the abnormality. Accordingly, by introducinglogical sum circuit block 67, it becomes possible to diagnose theabnormality of both the driver circuit 15 and the angular velocitydetection circuit at the same time.

By adopting the aforementioned construction, it is unnecessary toprovide any additional means for diagnosis such as an electrode forpseudo-driving on the sensor element 40. Also, it becomes easy to designelectrodes with improved driving efficiency when a smaller size sensorelement is required. Further, an angular velocity sensor with highperformance of abnormality detection can be realized.

In FIG. 27, waveforms at various circuit points, when the externaldiagnosis request signal is inputted (waveform o), are also shown byadding a letter O to the name of each point (as h_(o), i_(o), j_(o),k_(o), etc.) for the sake of easier understanding. These waveforms arebasically the same as shown in FIG. 21.

Twelfth Exemplary Embodiment

FIG. 28(a) is a circuit diagram of an angular velocity sensor inaccordance with a twelfth exemplary embodiment of the present invention.FIG. 28(b) shows electrostatic coupling capacitances formed between eachelectrode in a cross section of the sensor element 40 of the presentembodiment cut by the W—W plane. In FIGS. 28(a) and 28(b), elementswhich have the same function as in FIGS. 20(a) and 20(b) are denoted bythe same reference numerals and a detailed explanation thereto isomitted.

The electrostatic coupling capacitors 58 a, 58 b, 58 c, 58 d, 58 e and58 f, shown in FIG. 28(b), sometimes modify intrinsic output signalsoutputted from the sensor element 40 and induce an undesirable offsetvoltage in the output angular velocity signal. The present embodimentrelates to an adjusting circuitry to eliminate such influence of theelectrostatic coupling capacitors 58 a, 58 b, 58 c, 58 d, 58 e and 58 f.

In FIG. 28(a), a signal generator 62 generates a signal for use in theadjusting operation. In order to improve accuracy of adjusting, thefrequency of the signal generated by signal generator 62 is setdifferent from the frequency of the characteristic vibration mode of thesensor element 40 so as not to induce vibration in the sensor.

The signal generated by signal generator 62 is supplied, as a positivepolarity signal, to driving electrode 47 for pseudo-driving. Also, it isinverted by driving circuit 15 and supplied to driving electrodes 43 and44 for pseudo-driving as a negative polarity signal. Here, thepseudo-driving means provides a test signal to the sensor element 40 foran adjusting operation, without vibrating the sensor element 40.

Owing to the coupling by electrostatic coupling capacitors 58 a, 58 b,58 c, 58 d, 58 e and 58 f formed between driving electrodes 43, 46 and47, detected signals from sensor element 40 are modified. The modifiedsignal is called a “coupled signal”.

Switches 55 and 56 select the polarity of the driving signal supplied toadjustor 36 a in response to the switching signal from digital adjustingcircuit 63. They switch, in accordance with the polarity of the coupledsignals detected at sensor element 40, the polarity of the quasi-drivingvoltage applied to driving electrodes 43, 46 and 47.

Switch 57 is for stopping the ordinary driving of the sensor element 40by breaking the self-driving closed loop during the adjusting operation.Switches 60 and 66 enable canceling the unwanted signal induced byelectrostatic coupling capacitors 58 a, 58 b, 58 c, 58 d, 58 e and 58 fby use of the signal supplied to adjustor 36 a. In this action switch 66is usually closed.

When the values of electrostatic coupling capacitors 58 a, 58 b, 58 c,58 d, 58 e and 58 f are small and negligible, a more stable monitorsignal (signal at point a) can be used by closing switch 60 in place ofclosing switch 66. By using the monitor signal, the initial value of theunwanted signal from sensor element 40 induced by electrostatic couplingcapacitors 58 a, 58 b, 58 c, 58 d, 58 e and 58 f can be adjusted.

Terminal 65 is provided in order to monitor the pseudo-driving signalapplied to sensor element 40 during the adjusting process. By usingterminal 65, it becomes unnecessary to touch test probes to solderedportions, thus avoiding damaging the soldered portions. Also, it becomespossible to avoid a spurious signal being picked up by the test probewhich becomes a new signal source and couples with the sensingelectrodes 44:and 45 of the sensor element 40.

Digital adjusting circuit 63 supplies a control signal to adjust gainand offset of low pass filter 23, thus adjusting the output level of thepresent angular velocity sensor at output terminal 24. Also, digitaladjusting circuit 63 digitally selects the adjusting signal by storingthe adjusting amount of adjustor 36 a and by controlling the switches55, 56, 60 and 66.

Operational waveforms of each part of the present angular velocitysensor before, during and after the adjusting operation are shown inFIGS. 29(a), 29(b) and 29(c), respectively. Each waveform shown in FIGS.29(a), 29(b) and 29(c) is essentially the same as that of FIG. 21. Whatdiffers is that, several waveforms are modified by the on/off signal ofswitch 57 and by the signal from signal generator 62. The state ofswitch 57 is shown by waveform indicated by sw, where a high level meansthe switch is closed. The operational state of signal generator 62 isshown by waveform indicated by sg, where a high level means the signalgenerator is in operation.

Current signals d and e, shown in FIG. 29(a), are modified byelectrostatic coupling capacitors 58 a, 58 b, 58 c, 58 d, 58 e and 58 fshown in FIG. 28(b). The capacitance value of electrostatic couplingcapacitors 58 a, 58 b, 58 c, 58 d, 58 e and 58 f varies easily caused bydifferences in shape, distance and position of each electrode, and bydifference in shape of the sensor element 40, resulting in a variationof the electrostatic coupling capacitors C. Current signals d and e notcanceled by differential amplifier 52 induce a differential coupledcurrent ·C·Vd (waveform at point h), where and Vd are respectively theangular frequency and amplitude of the driving voltage. This signal atpoint h is phase shifted by 90 degrees phase shifter 53 and is inputtedto synchronous detector 22 as a signal with the same phase as themonitor signal (waveform at point a), and is finally outputted to outputterminal 24 as an offset voltage V.

As the offset voltage is proportional to ·C·Vd, the driving voltage isan important factor in generating the offset voltage. Because theamplitude of the driving voltage is determined automatically by thedriving closed loop including sensor element 40, the driving voltage iseasily affected by various factors such as a temperature dependence ofthe piezoelectric property of the material constructing sensor element40. Piezoelectric property of crystal material especially showsexponential increase with temperature.

Thus, if the sensor element 40 has a non-negligible level of coupling,the offset voltage of an output of the sensor shows a non-lineartemperature dependence in a higher temperature range. Accordinglycompensation means becomes complicated. Also, if the characteristics ofthe sensor varies with time it directly generates the variation in theoffset voltage and the reliability of the sensor becomes poor.

In order to prevent this offset voltage variation, the present inventionintroduces a test period for forcibly stopping the vibration of sensorelement 40, to which quasi-driving voltages b and c are supplied from asignal generator 62. In the test period, adjustor 36 a works to reducethe signal at point h or i which is proportional to the differencebetween two output current signals d and e induced by electrostaticcoupling capacitors 58 a, 58 b, 58 c, 58 d, 58 e and 58 f. By doing so,the accuracy of adjusting, and as a result, the accuracy of the sensoris improved. The frequency of the quasi-driving signal from signalgenerator 62 may be selected to be other than the characteristicvibration frequency of the sensor element 40.

Now the process for reducing V is explained when a ladder networkresistor is used as adjustor 36 a and capacitor 37 b is used as aninjector for compensation. As shown in FIG. 29(b), quasi-driving voltageb and c with a trapezoidal waveform are generated when signal generatoris in a working state. Denoting a capacitance of capacitor 37 b as C anda constant of ladder network resistor used for reducing V as, the amountof adjusting signal is expressed by formula (13).

C·Vd  (13)

Accordingly, by adjusting so as to make the amount expressed by formula(14) zero, the waveforms at point h and point i reach zero as shown inFIG. 29(b), supposing C and C are stable, against temperature.

C·Vd−C·Vd=(C−C·)·Vd  (14)

As a result, after the above-mentioned adjusting operation, thewaveforms at point h, i and j become almost zero as shown in FIG. 29(c)and the offset voltage V, in which the influence of driving voltage Vdis suppressed, is outputted to output terminal 24.

By integrating capacitor 37 b into a semiconductor integrated circuittogether with other circuit blocks, portions connected by soldering arereduced and the reliability of the sensor is further improved.

During the adjusting period, is usually determined so as to adjust thesignal level (at point i) of terminal 64 to zero, by monitoring thepseudo-driving signal at terminal 65 and the signal at terminal 64 usingan oscilloscope or the like. The adjustment is performed by successivelysending digital data to the ladder network resistor and finding theoptimum digital data that gives zero differential voltage at terminal 64induced by the current signal d and e. The obtained optimum digital datais stored in a memory such as ROM. Thus, a highly accurate sensor, inwhich the influence of the electrostatic coupling capacitors 58 a, 58 b,58 c, 58 d, 58 e and 58 f is suppressed in a normal operating condition,can be obtained.

Although in this exemplary embodiment only the case in which the offsetvoltage V at output terminal 24 is set to infinitesimally zero byadjusting is explained, it is also possible to set the offset voltage Vto a non-zero definite value by adjusting . Also, by using a temperaturesensitive device as the ladder network resistor and capacitor 37 b, itis possible to perform the adjusting so as to include temperaturecompensation.

Although in this exemplary embodiment explanation is made only forcrystal or quartz as a sensor element 40, it is also possible to usepiezoelectric ceramics, silicon, or the combination of silicon andpiezoelectric film as the vibrator material.

Also, although the construction of the present invention with respect tothe eighth through twelfth exemplary embodiments was described using acurrent amplifier, differential amplifier, phase shifter and synchronousdetector, the present invention is not limited to this construction. Inparticular, any synchronous demodulator that can synchronously detectthe output of a differential amplifier and outputs the angular velocitysignal, such as the circuit block combining a detector and phaseshifter, can be used.

Thirteenth Exemplary Embodiment

FIG. 30 is a circuit diagram of an angular velocity sensor in accordancewith a thirteenth exemplary embodiment of the present invention. In FIG.30, elements which have the same function as in FIG. 20(a) are denotedby the same reference numerals and a detailed explanation thereto isomitted.

In FIG. 30, synchronous demodulator 69 shifts the phase of thedifference of the outputs of current amplifiers 50 and 51 by 90 degrees,then sample-holds the shifted signal, and finally synchronously detectsthe sample-held signal. As synchronous demodulator 69 contains thesample-hold function, saturation of the circuit caused by excessiveunwanted signals generated in sensor element 40 can be avoided.

Although in this exemplary embodiment, explanation is made on thesynchronous demodulator including a 90 degrees phase shifter,sample-holder, and synchronous detector, the present invention is notlimited to this construction. Any circuit block which functions for thesame purpose can be used instead.

Thus, an angular velocity sensor of the present invention can detectfrom a state of the mechanical coupling signal whether the angularvelocity signal is in a state which can perform a correct detection ornot. Moreover, because the mechanical coupling signal is alwaysgenerated, it is unnecessary to provide independent means for generatingthe mechanical coupling signal and the composition of the sensor becomesvery simple and highly reliable for self diagnosis.

What is claimed is:
 1. An angular velocity sensor comprising: a sensorincluding a vibrator and a detector for detecting an angular velocity; adrive unit including a driver circuit and a monitor circuit, whereinsaid driver circuit supplies a driving signal to the vibrator part ofsaid sensor, and said monitor circuit receives a monitor signal fromsaid sensor; detection unit including an amplifier unit and asynchronous demodulator, wherein said amplifier unit receives outputsfrom the detector of said sensor and wherein said synchronousdemodulator sample-holds an output from said amplifier unit insynchronous with the driving signal or the monitor signal from saiddrive unit and outputs an angular velocity signal; and self diagnosisunit which provides a diagnosis signal to detect an abnormality of atleast one of said sensor, said detection unit and said drive unit byproviding a displacement signal synchronized with said driving signal orsaid monitor signal to said detection unit.
 2. An angular velocitysensor according to claim 1, wherein said self diagnosis unit comprisesan attenuator for attenuating said signal synchronized with said drivingsignal or said monitor signal to generate said displacement signal, andan injector for providing said displacement signal from said attenuatorto said detection unit.
 3. An angular velocity sensor according to claim2, further including a changing unit for changing said self diagnosisunit to either a working state or a non-working state, said changingunit disposed between said attenuator and said injector.
 4. An angularvelocity sensor according to claim 3, further including a judging unitfor continuously judging an abnormality of said sensor element bydetecting an output level of said detection unit during the non-workingstate of said self diagnosis unit.
 5. An angular velocity sensoraccording to claim 3, wherein said changing unit is a switch forconnecting or disconnecting, in accordance with an external signal, saidsignal synchronized with said driving signal to a circuit, said circuithaving an output coupled to said synchronous detector.
 6. An angularvelocity sensor according to claim 3, wherein said changing unitcomprises a timer circuit for connecting or disconnecting for a giventime, in accordance with an external signal, said signal synchronizedwith said driving signal to a circuit, said circuit having an outputcoupled to said synchronous detector.
 7. An angular velocity sensoraccording to claim 2, wherein said injector comprises a capacitor.
 8. Anangular velocity sensor according to claim 2, wherein said injectorcomprises a resistor.
 9. An angular velocity sensor according to claim2, wherein said attenuator includes a ladder network resistor capable ofdigitally adjusting an amplitude and/or phase of an input signal.
 10. Anangular velocity sensor according to claim 2, further including abalancing unit, wherein said balancing unit is disposed at an inputterminal of one of said pair of current amplifiers and said inputterminal is not connected to said injector, in order to keep a balanceof input characteristics between each of said pair of currentamplifiers.